The area where a phenolic spacer would probably work best on these cars is between the engine and the intake manifold rather than between the manifold and the throttle body.

In the past I've always just made my own, since they're not that difficult. Just trace your intake manifold gaskets onto some teflon skived sheeting in 1/8" thickness and you should be all set to cut and install (remember 1/8" longer mounting bolts however).